As in the patents to Muller U.S. Pat. No. 2,434,427, Parks U.S. Pat. No. 2,765,868, Bouskill U.S. Pat. No. 3,396,825 and Morrison U.S. Pat. No. 3,447,684, filter assemblies in which dual filter units alternate manually or automatically in filtering and regeneration, are commonly used for filtering fluids in installations requiring an uninterrupted output of filtered fluid. Also, in such assemblies it is not uncommon to employ a reverse flow of filtered fluid from the then filtering filter unit, either alone or supplemented by heating or otherwise, for regenerating the desiccant or other filter medium in the other, then inactive, filter unit. The present invention is directed to improvements in such filter assemblies and particularly those having molecular sieve or other desiccants for selectively adsorbing moisture or other contaminants from compressed gas.